Work machine and method for controlling work machine

ABSTRACT

A work machine includes a vehicle body, a lift frame rotatably supported around a lift axis with respect to the vehicle body, a blade rotatably supported around a pitch axis with respect to the lift frame, a lift actuator connected to the lift frame and the vehicle body, a pitch actuator connected to the blade and the lift frame, a sensor that detects a height of the blade from a reference height determined based on the vehicle body, and a controller that controls the pitch actuator to change a pitch angle of the blade according to the height of the blade. The lift actuator causes the lift frame to perform a lift motion up and down around the lift axis. The pitch actuator causes the blade to perform a pitching motion around the pitch axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of International Application No. PCT/JP2022/011358, filed on Mar. 14, 2022. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2021-076600, filed in Japan on Apr. 28, 2021, the entire contents of which are hereby incorporated herein by reference.

BACKGROUND Field of the Invention

The present invention relates to a work machine and a method for controlling a work machine.

Background Information

Some work machines can adjust the pitch angle of the blade according to the operation of the operator. For example, the work machine of JP-A-7-252859 is provided with an operation lever for adjusting the pitch angle of the blade. A switch is provided on the operating lever. When the switch is on and the operating lever is pushed to the right, the hydraulic cylinder is controlled so that the blade performs a pitch dump motion (tilts forward). When the switch is on and the operating lever is pushed to the left, the hydraulic cylinder is controlled so that the blade performs a pitch back motion (tilts rearward).

SUMMARY

The pitch angle of the blade affects workability such as excavation or leveling. However, the pitch angle of the blade differs depending on the type of work. For example, when the pitch angle is large, that is, when the blade is tilted forward, the leveling performance is good, but the digging resistance is high and thereby the digging performance is low. When the pitch angle is small, that is, when the blade is tilted backward, the digging resistance is small and thereby the digging performance is good, but the soil spillage to the rear of the blade is high and the leveling performance is low.

Therefore, it is not easy for even a skilled operator to manually select an appropriate pitch angle accurately. An object of the present disclosure is to enable easy and appropriate adjustment of a pitch angle of a blade in a work machine.

A work machine according to a first aspect of the present disclosure includes a vehicle body, a lift frame, a blade, a lift actuator, a pitch actuator, a sensor, and a controller. The lift frame is supported rotatably around a lift axis with respect to the vehicle body. The blade is rotatably supported around a pitch axis with respect to the lift frame. The lift actuator is connected to the lift frame and the vehicle body, and causes the lift frame to perform a lift motion up and down around the lift axis. The pitch actuator is connected to the blade and the lift frame, and causes the blade to perform a pitching motion around the pitch axis. The sensor detects a height of the blade from a reference height determined based on the vehicle body. The controller controls the pitch actuator to change the pitch angle of the blade according to the height of the blade.

A method according to a second aspect of the present disclosure is a method for controlling a work machine. The work machine includes a vehicle body, a lift frame, a blade, a lift actuator, and a pitch actuator. The lift frame is supported rotatably around a lift axis with respect to the vehicle body. The blade is rotatably supported around a pitch axis with respect to the lift frame. The lift actuator is connected to the lift frame and the vehicle body, and causes the lift frame to perform a lift motion up and down around the lift axis. The pitch actuator is connected to the blade and the lift frame, and causes the blade to perform a pitching motion around the pitch axis. The method includes detecting a height of the blade from a reference height determined based on the vehicle body, and controlling the pitch actuator to change the pitch angle of the blade according to the height of the blade.

According to the present disclosure, the pitch actuator is automatically controlled to change the pitch angle of the blade depending on the height of the blade. Thereby, the pitch angle of the blade can be easily and appropriately adjusted in the work machine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a work machine according to an embodiment.

FIG. 2 is a block diagram showing a structure of a drive system and a control system of the work machine.

FIG. 3 is a diagram showing a height of a blade from a reference height.

FIG. 4A, FIG. 4B and FIG. 4C are diagrams showing pitch angles of the blade.

FIG. 5 is a diagram showing an example of pitch angle data.

FIG. 6 is a diagram showing a pitching motion of the blade when the height of the blade is equal to or greater than the reference height.

FIG. 7 is a diagram showing the pitching motion of the blade when the height of the blade is below the reference height.

DETAILED DESCRIPTION OF EMBODIMENT(S)

A work machine according to an embodiment will be described below with reference to the drawings. FIG. 1 is a side view showing a work machine 1 according to an embodiment. The work machine 1 according to the present embodiment is a bulldozer. The work machine 1 includes a vehicle body 11 and a work implement 12.

The vehicle body 11 includes an operator's cab 13, an engine compartment 14, and a travel device 15. A driver's seat (not shown) is disposed in the operator's cab 13. The engine compartment 14 is disposed in front of the operator's cab 13. The travel device 15 is provided under the vehicle body 11. The travel device 15 includes a pair of left and right crawler belts 16. Note that FIG. 1 shows only the left crawler belt 16. The work machine 1 runs by rotating the crawler belt 16.

The work implement 12 is attached to the vehicle body 11. The work implement 12 includes a lift frame 17, a blade 18, a lift actuator 19, and a pitch actuator 20. The lift frame 17 is rotatably supported with respect to the vehicle body 11 around a lift axis X1. The lift axis X1 extends in the lateral direction of the vehicle body 11. The lift frame 17 rotates around the lift axis X1 to perform a lift motion up and down.

The blade 18 is disposed in front of the vehicle body 11. The blade 18 is rotatably supported on the lift frame 17 around a pitch axis X2. The pitch axis X2 extends in the lateral direction of the vehicle body 11. The blade 18 rotates around the pitch axis X2 to perform a pitching motion forward and backward. The blade 18 moves up and down as the lift frame 17 moves up and down.

The lift actuator 19 is connected to the vehicle body 11 and the lift frame 17. The lift actuator 19 is a hydraulic cylinder. Expansion and contraction of the lift actuator 19 causes the lift frame 17 to perform the lift motion up and down. As the lift actuator 19 contracts, the blade 18 raises. As the lift actuator 19 expands, the blade 18 lowers.

The pitch actuator 20 is connected to lift frame 17 and blade 18. The pitch actuator 20 is a hydraulic cylinder. Expansion and contraction of the pitch actuator 20 causes the blade 18 to perform the pitching motion forward and backward. A portion of the blade 18, for example, the upper end, moves back and forth to allow the blade 18 to perform the pitching motion around the pitch axis X2. As the pitch actuator 20 expands, the blade 18 tilts forward. As the pitch actuator 20 contracts, the blade 18 tilts backward.

FIG. 2 is a block diagram showing a configuration of a drive system 2 and a control system 3 of the work machine 1. As shown in FIG. 2 , the drive system 2 includes an engine 22, a hydraulic pump 23, and a power transmission device 24. The hydraulic pump 23 is driven by the engine 22 and discharges hydraulic fluid. The hydraulic fluid discharged from the hydraulic pump 23 is supplied to the lift actuator 19 and the pitch actuator 20. Although one hydraulic pump is illustrated in FIG. 2 , a plurality of hydraulic pumps may be provided.

The power transmission device 24 transmits the driving force of the engine 22 to the travel device 15. The power transmission device 24 may be, for example, an HST (Hydro Static Transmission). Alternatively, the power transmission device 24 may be, for example, a torque converter or a transmission with a plurality of gears.

The control system 3 includes a controller 26 and a control valve 27. The controller 26 is programmed to control the work machine 1 based on the acquired data. The controller 26 includes a storage device 28 and a processor 29. The processor 29 includes, for example, a CPU. The storage device 28 includes, for example, a memory and an auxiliary storage device. The storage device 28 may be, for example, RAM or ROM. The storage device 28 may be a semiconductor memory, a hard disk, or the like. The storage device 28 is an example of a non-transitory computer-readable recording medium. The storage device 28 stores computer instructions executable by the processor 29 to control the work machine 1.

The control valve 27 is a proportional control valve and is controlled by a command signal from the controller 26. The control valve 27 is disposed between hydraulic actuators, such as the lift actuator 19 and the pitch actuator 20, and the hydraulic pump 23. The control valve 27 controls the flow rate of hydraulic fluid supplied from the hydraulic pump 23 to the lift actuator 19. The control valve 27 controls the flow rate of hydraulic fluid supplied from the hydraulic pump 23 to the pitch actuator 20. Note that the control valve 27 may be a pressure proportional control valve. Alternatively, the control valve 27 may be an electromagnetic proportional control valve.

The control system 3 includes an operating device 31 and an input device 32. The operating device 31 includes, for example, a lever. Alternatively, the operating device 31 may include a pedal or a switch. An operator can use the operating device 31 to manually operate the travel of the work machine 1 and the operation of the work implement 12. The operating device 31 outputs an operation signal indicating the operation of the operating device 31. The controller 26 receives the operation signal from the operating device 31.

The operating device 31 can operate the lift motion of the blade 18. Specifically, the operating device 31 is operable in a raising operation and a lowering operation for the blade 18. When the operator perform the raising operation to the operating device 31, the controller 26 controls the lift actuator 19 so that the blade 18 is raised. When the operator performs the lowering operation to the operating device 31, the controller 26 controls the lift actuator 19 so that the blade 18 is lowered.

The operating device 31 can operate the pitching motion of the blade 18. Specifically, the operating device 31 is operable in a forward tilting operation and a backward tilting operation for the blade 18. When the operator performs the forward tilting operation to the operating device 31, the controller 26 controls the pitch actuator 20 so that the blade 18 tilts forward. When the operator performs the backward tilting operation to the operating device 31, the controller 26 controls the pitch actuator 20 so that the blade 18 tilts backward.

Note that the operating device 31 may be a hydraulic pilot type device. For example, the operating device 31 may output pilot hydraulic pressure according to the operation of the operating device 31. The lift actuator 19 or the pitch actuator 20 may be controlled by controlling the control valve 27 with the pilot hydraulic pressure from the operating device 31. The controller 26 may receive a signal indicating the pilot hydraulic pressure as the operation signal.

The input device 32 includes, for example, a touch screen. However, input device 32 may include other devices such as a switch. The operator can use the operating device 31 to set the control mode of the pitch angle of the blade 18 by the controller 26. The control mode for the pitch angle of the blade 18 will be described later in detail.

The control system 3 includes a sensor 33 that detects a height of the blade 18. The sensor 33 include a vehicle body sensor 34, a frame sensor 35, and a blade sensor 36. The vehicle body sensor 34 is attached to the vehicle body 11. The vehicle body sensor 34 detects an attitude of the vehicle body 11. The frame sensor 35 is attached to the lift frame 17. The frame sensor 35 detects an attitude of the lift frame 17. The blade sensor 36 is attached to the blade 18. The blade sensor 36 detects an attitude of the blade 18.

The vehicle body sensor 34, the frame sensor 35, and the blade sensor 36 are each an IMU (Inertial Measurement Unit). However, the frame sensor 35 and the blade sensor 36 are not limited to the IMU, and may be other sensors such as an angle sensor or a cylinder stroke sensor.

The vehicle body sensor 34 detects an angle (vehicle pitch angle) of the vehicle body 11 in the front-rear direction with respect to the horizontal. The frame sensor 35 detects a rotation angle of the lift frame 17. The blade sensor 36 detects a pitch angle of the blade 18. The vehicle body sensor 34, the frame sensor 35, and the blade sensor 36 each output a detection signal indicating the detected angle.

The controller 26 receives the detection signals from the vehicle body sensor 34, the frame sensor 35, and the blade sensor 36. The controller 26 calculates the height of the blade 18 from a reference height H0 determined based on the vehicle body 11 based on the detection signals. As shown in FIG. 3 , the reference height H0 is a height of the ground contact surface G1 of the crawler belt 16. The height of the blade 18 is a height of the cutting edge P0 of the blade 18 from the ground contact surface G1.

The controller 26 stores machine dimension data indicating dimensions and positional relationships among the vehicle body 11, the lift frame 17, and the blade 18. The controller 26 calculates the height of the blade 18 from the reference height H0 based on the angles detected by the vehicle body sensor 34, the frame sensor 35, and the blade sensor 36, and the machine dimension data.

As shown in FIG. 3 , the height of the blade 18 is zero when the cutting edge P0 of the blade 18 is placed on the ground contact surface G1 of the crawler belt 16. When the cutting edge P0 of the blade 18 is positioned above the ground contact surface G1 of the crawler belt 16, the height of the blade 18 is a positive value. When the cutting edge P0 of the blade 18 is positioned below the ground contact surface G1 of the crawler belt 16, the height of the blade 18 is a negative value. In FIG. 3 , P1 indicates the highest position of the cutting edge P0 of the blade 18. P2 indicates the lowest position of the cutting edge P0 of the blade 18. The work machine 1 can causes the blade 18 to perform the lift motion between the highest position P1 and the lowest position P2.

Next, the control mode of the pitch angle of the blade 18 will be explained. The control mode of the pitch angle of the blade 18 includes an automatic mode and a manual mode. The controller 26 switches between the automatic mode and the manual mode according to the operation of the input device 32. The operator can select between the automatic mode and the manual mode by operating the input device 32.

In the automatic mode, the controller 26 controls the pitch actuator 20 to change the pitch angle of the blade 18 according to the height of the blade 18 from the reference height H0. FIGS. 4A to 4C are diagrams showing the pitch angles of the blade 18. As shown in FIGS. 4A to 4C, the pitch angles θ1-θ3 of the blade 18 are angles between the cutting edge P0 of the blade 18 and the ground contact surface G1 of the crawler belt 16. FIG. 4B shows the pitch angle θ2 of the blade 18 in a standard state. FIG. 4A shows the pitch angle θ1 of the blade 18 tilted forward from the standard state. FIG. 4C shows the pitch angle θ3 of the blade 18 tilted backward from the standard state. The pitch angle increases as the blade 18 tilts forward. The pitch angle decreases as the blade 18 tilts backward. That is, θ1>θ2>θ3.

The controller 26 stores pitch angle data. The pitch angle data defines a relationship between the height of the blade 18 and a target pitch angle of the blade 18. The pitch angle data is stored in the controller 26 in a form of a map, for example. However, the pitch angle data may be stored in the controller 26 in other formats such as formulas, not limited to maps.

The controller 26 refers to the pitch angle data and determines the target pitch angle from the height of the blade 18. The controller 26 controls the pitch actuator 20 so that the pitch angle of the blade 18 becomes the target pitch angle. FIG. 5 is a diagram showing an example of the pitch angle data. The solid line in FIG. 5 indicates an example of the pitch angle data in the present embodiment.

In FIG. 5 , the chain double-dashed line indicates changes in the pitch angle when the control mode of the pitch angle is not performed. That is, the chain double-dashed line in FIG. 5 indicates changes in the pitch angle when the pitching motion of the blade 18 is fixed (hereinafter referred to as the pitch angle in a non-controlled state). When the pitching motion is fixed, the pitch angle changes in proportion to the change in the height of the blade 18 between the maximum value Hmax and the minimum value Hmin, as indicated by the two-dot chain line in FIG. 5 . The change in the pitch angle in the non-controlled state indicates the change in the pitch angle due to the rotation of the lift frame 17 around the lift axis X1. The pitch angle in the non-controlled state decreases at a constant rate as the height of the blade 18 increases.

On the other hand, the pitch angle data in the automatic mode in the present embodiment defines the target pitch angle larger than the pitch angle in the non-controlled state with respect to the height of the blade 18 that is greater than zero. Therefore, as shown in FIG. 6 , the controller 26 controls the pitch actuator 20 to tilt the blade 18 forward more than that in the non-controlled state when the blade 18 is positioned above the reference height H0. In FIG. 6 , the two-dot chain line indicates the posture of the blade 18 in the non-controlled state.

Further, as shown in FIG. 5 , the absolute value of the inclination of the pitch angle data when the height of the blade 18 is in a first range (0-H1) is larger than that in the non-controlled state. The first range (0-H1) is a range from 0 to H1 for the height of the blade 18. H1 is a value between 0 and Hmax. The absolute value of the inclination of the pitch angle data when the height of the blade 18 is in a second range (H1-Hmax) is the same as that in the non-controlled state. The second range is a range from H1 to Hmax for the height of the blade 18.

When the height of the blade 18 is within the first range (0-H1), the controller 26 changes the pitch angle of the blade 18 in a direction of tilting the blade 18 forward according to the increase in the height of the blade 18. The controller 26 fixes the pitching motion of the blade 18 by the pitch actuator 20 when the height of blade 18 is within the second range (H1-Hmax).

The pitch angle data in the automatic mode in the present embodiment defines the target pitch angle that is smaller than the pitch angle in the non-controlled state with respect to the height of the blade 18 that is smaller than zero. Therefore, as shown in FIG. 7 , the controller 26 controls the pitch actuator 20 so that the blade 18 is tilted more backward than that in the non-controlled state when the blade 18 is positioned below the reference height H0. In FIG. 7 , the two-dot chain line indicates the posture of the blade 18 in the non-controlled state.

Also, as shown in FIG. 5 , when the height of the blade 18 is within a third range (0-H2), the pitch angle decreases as the height of the blade 18 decreases. The third range (0-H2) is a range from 0 to H2 for the height of the blade 18. H2 is a value between 0 and Hmin. The absolute value of the inclination of the pitch angle data when the height of the blade 18 is in a fourth range (H2-Hmin) is the same as that in the non-controlled state. The fourth range (H2-Hmin) is a range from H2 to Hmin for the height of the blade 18.

When the height of the blade 18 is within the third range (0-H2), the controller 26 changes the pitch angle of the blade 18 in a direction of tilting the blade 18 backward according to the decrease in the height of the blade 18. The controller 26 fixes the pitching motion of the blade 18 by the pitch actuator 20 when the height of the blade 18 is within the fourth range (H2-Hmin).

In the manual mode, the pitch actuator 20 is controlled so as to change the pitch angle of the blade 18 according to the operation of the operating device 31. When the operating device 31 is not operated, the pitch actuator 20 is controlled so as to maintain the pitch angle of the blade 18. For example, when the operating device 31 is not operated, the controller 26 controls the pitch actuator 20 so as to maintain the pitch angle of the blade 18 even if some hydraulic fluid leaks from the control valve 27.

In the work machine 1 according to the present embodiment described above, the pitch actuator 20 is automatically controlled to change the pitch angle of the blade 18 according to the height of the blade 18 in the automatic mode. Thereby, in the work machine 1, the pitch angle of the blade 18 can be adjusted easily and appropriately.

For example, when the blade 18 is positioned above the reference height H0, the pitch actuator 20 is controlled to tilt the blade 18 forward more than that in the non-controlled state. When the blade 18 is positioned above the reference height H0, ground leveling or dumping work is often performed. Therefore, when the blade 18 is positioned above the reference height H0, the blade 18 tilts forward, thereby improving workability in the ground leveling or dumping work.

Further, when the blade 18 is positioned below the reference height H0, the pitch actuator 20 is controlled to tilt the blade 18 rearward more than that in the non-controlled state. Excavation work is often performed when the blade 18 is positioned below the reference height H0. Therefore, when the blade 18 is positioned below the reference height H0, the blade 18 tilts backward, thereby improving workability in the excavation work.

As described above, in the work machine 1 according to the present embodiment described above, the automatic mode allows the pitch angle of the blade 18 to be easily and appropriately adjusted according to the content of the work.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the invention.

The work machine 1 is not limited to a bulldozer, and may be other vehicles such as a wheel loader and a motor grader. The controller 26 may have a plurality of controllers separate from each other. The processing by the controller 26 is not limited to the above embodiment, and may be modified. A part of the processing in the automatic mode or the manual mode described above may be omitted. Alternatively, a part of the processing described above may be changed.

The lift actuator 19 and the pitch actuator 20 are not limited to hydraulic cylinders. The lift actuator 19 and the pitch actuator 20 may be other actuators such as electric motors, for example. The pitch angle data are not limited to those in the above embodiment, and may be changed. For example, the pitch angle data may have the inclination different from that in the non-controlled state in the second range. The pitch angle data may have the inclination different from that in the non-controlled state in the fourth range.

According to the present disclosure, the pitch angle of the blade can be easily and appropriately adjusted in the work machine. 

1. A work machine comprising: a vehicle body; a lift frame rotatably supported around a lift axis with respect to the vehicle body; a blade rotatably supported around a pitch axis with respect to the lift frame; a lift actuator connected to the lift frame and the vehicle body, the lift actuator being configured to cause the lift frame to perform a lift motion up and down around the lift axis; a pitch actuator connected to the blade and the lift frame, the pitch actuator being configured to cause the blade to perform a pitching motion around the pitch axis; a sensor configured to detect a height of the blade from a reference height determined based on the vehicle body; and a controller configured to control the pitch actuator to change a pitch angle of the blade according to the height of the blade.
 2. The work machine according to claim 1, wherein the controller is configured to control the pitch actuator to tilt the blade more forward when the blade is positioned above the reference height than when the pitching motion of the blade is fixed.
 3. The work machine according to claim 2, wherein when the blade is positioned above the reference height, the controller is configured to control the pitch actuator to change the pitch angle of the blade in a direction to tilt the blade forward according to increasing in the height of the blade.
 4. The work machine according to claim 1, wherein the controller is configured to control the pitch actuator to tilt the blade more rearward when the blade is positioned below the reference height than when the pitching motion of the blade is fixed.
 5. The work machine according to claim 4, wherein when the blade is positioned below the reference height, the controller is configured to control the actuator to change the pitch angle of the blade in a direction of tilting the blade backward in accordance with decreasing in the height of the blade.
 6. The work machine according to claim 1, wherein the vehicle body includes a crawler belt, and the reference height is a height of a ground contact surface of the crawler belt.
 7. The work machine according to claim 1, wherein the controller is configured to store pitch angle data that defines a relationship between the height of the blade and a target pitch angle of the blade, determine the target pitch angle from the height of the blade with reference to the pitch angle data, and control the pitch actuator so that the pitch angle of the blade becomes the target pitch angle.
 8. The work machine according to claim 1, further comprising: an operating device for manually operating the pitch angle of the blade, the controller being configured to acquire an operation signal indicating an operation of the operating device, control the pitch actuator to change the pitch angle of the blade according to the operation of the operating device, and control the pitch actuator to maintain the pitch angle of the blade when the operating device is not operated.
 9. A method for controlling a work machine, the work machine including a vehicle body, a lift frame rotatably supported with respect to the vehicle body around a lift axis, a blade rotatably supported with respect to the lift frame around a pitch axis, a lift actuator connected to the lift frame and the vehicle body, the lift actuator being configured to cause the lift frame to perform a lift motion up and down around the lift axis, and a pitch actuator connected to the blade and the lift frame, the pitch actuator being configured to case the blade to perform a pitching motion around the pitch axis, the method comprising: detecting a height of the blade from a reference height determined based on the vehicle body; and controlling the pitch actuator to change a pitch angle of the blade according to the height of the blade.
 10. The method according to claim 9, further comprising: controlling the pitch actuator to tilt the blade more forward when the blade is positioned above the reference height than when the pitching motion of the blade is fixed.
 11. The method according to claim 10, further comprising: controlling the pitch actuator to change the pitch angle of the blade in a direction of tilting the blade forward according to increasing in the height of the blade when the blade is positioned above the reference height.
 12. The method according to claim 9, further comprising: controlling the pitch actuator to tilt the blade more rearward when the blade is positioned below the reference height than when the pitching motion of the blade is fixed.
 13. The method according to claim 12, further comprising: controlling the pitch actuator to change the pitch angle of the blade in a direction of tilting the blade backward in accordance with decreasing in the height of the blade when the blade is positioned below the reference height.
 14. The method according to claim 9, wherein the vehicle body includes a crawler belt, and the reference height is a height of a ground contact surface of the crawler belt.
 15. The method according to claim 9, further comprising: determining a target pitch angle from the height of the blade with reference to pitch angle data that defines a relationship between the height of the blade and the target pitch angle of the blade; and controlling the pitch actuator so that the pitch angle of the blade becomes the target pitch angle.
 16. The method according to claim 9, further comprising: obtaining an operation signal indicating operation of an operating device for manually operating the pitch angle of the blade; controlling the pitch actuator to change the pitch angle of the blade according to the operation of the operating device; and controlling the pitch actuator to maintain the pitch angle of the blade when the operating device is not operated. 